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1.
Changes in the level of hydrogen peroxide (H2O2) and activity of peroxidases towards phenolic substrates (EC 1.11.1.7) such as pyrogallol (PPX), syringaldazine (SPX) and guaiacol (GPX), and cytosolic ascorbate peroxidase (cAPX, EC 1.11.1.11) in response to infestation of cowpea aphid (Aphis craccivora Koch) were analyzed in soybean (Glycine max (L.) Merr. cv. “Nam Dan”) at the V3 stage (first two trifoliate leaves fully developed, third trifoliate leaf unrolled) for 96 h post-infestation (hpi). Influence of A. craccivora at a varied population size (10, 20 and 30 individuals per each soybean plant) caused a burst of H2O2 generation in the aphid-infested leaves at 12 hpi. Paralleling the H2O2 accumulation, peroxidase activity in all the infested plants remarkably increased and was significantly higher than that observed in controls (uninfested plants). The cascade of enzymes induced was continuously overlapped by the early enhancement of SPX within 6–24 hpi, an expression of cAPX (12–48 hpi) followed by an accumulation of GPX (24–72 hpi) and PPX (24–96 hpi). The differential induction of SPX, GPX, PPX and cAPX resulted in a rapid reduction of H2O2 content in aphid-infested leaves, and the activity of peroxidase was closely correlated with the intensity of A. craccivora infestation around the defined points of time at which the activity of each enzyme reached the maximum level. The increase in activity of peroxidases matched their function as controlling accumulation of H2O2 and detoxifying this reactive oxygen product when soybean plants were challenged with cowpea aphid. Furthermore, peroxidases could directly deter cowpea aphid feeding through other functions such as the anti-nutritive and/or toxicological defenses and/or limiting the penetration of aphid stylets into plant tissues via participating to strengthen and reinforce the cell wall barrier. These results indicated that peroxidases may be some elements of the defense system that increased the resistance of G. max cv. “Nam Dan” to infestation of A. craccivora.  相似文献   

2.
Abscisic acid (ABA) and hydrogen peroxide (H2O2) are important regulatory factors involved in plant development under adversity stress. Here, the involvement of H2O2 in ABA-induced adventitious root formation in cucumber (Cucumis sativus L.) under drought stress was determined. The results indicated that exogenous ABA or H2O2 promoted adventitious rooting under drought stress, with a maximal biological response at 0.5 μM ABA or 800 μM H2O2. The promotive effects of ABA-induced adventitious rooting under drought stress were suppressed by CAT or DPI, suggesting that endogenous H2O2 might be involved in ABA-induced adventitious rooting. ABA increased relative water content (RWC), leaf chlorophyll content, chlorophyll fluorescence parameters (Fv/Fm, ΦPS II and qP), water soluble carbohydrate (WSC) and soluble protein content, and peroxidase (POD), polyphenol oxidase (PPO) and indoleacetate oxidase (IAAO) activities, while decreasing transpiration rate. However, the effects of ABA were inhibited by H2O2 scavenger CAT. Therefore, H2O2 may be involved in ABA-induced adventitious root development under drought stress by stimulating water and chlorophyll content, chlorophyll fluorescence, carbohydrate and nitrogen content, as well as some enzyme activities.  相似文献   

3.
A derivative of Rhizobium japonicum (strain 122 DES) has been isolated which forms nodules on soybeans that evolve little or no H2 in air and efficiently fixes N2. Bacteroids isolated from nodules formed by strain 122 DES took up H2 with O2 as the physiological acceptor and appeared to be typical of those R. japonicum strains that possess the H2 uptake system. The hydrogenase system in soybean nodules is located within the bacteroids and activity in macerated bacteroids is concentrated in a particulate fraction. The pH optimum for the reaction is near 8.0 and apparent K m values for H2 and O2 are 2 M and 1 M, respectively. The H2 oxidizing activity of a suspension of 122 DES bacteroids was stable at 4°C for at least 4 weeks and was not particularly sensitive to O2. Neither C2H2 nor CO inhibited O2 dependent H2 uptake activity.Non-physiological electron acceptors of positive oxidation reduction potential also supported H2 uptake by bacteroids. The rate of H2 uptake with phenazine methosulfate as the acceptor was greater than that with O2. When methylene blue, triphenyltetrazolium, potassium ferricyanide or dichlorophenolindophenol were added to bacteriod suspensions, without preincubation, rates of H2 uptake were supported that were lower than those in the presence of O2. Preincubation of the bacteroids with acceptors increased the rates of H2 uptake. No H2 evolution was observed from reaction mixtures containing bacteroid suspensions and reduced methyl or benzyl viologens. Of a series of carbon substrates added to bacteroid suspensions only acetate, formate or succinate at concentrations of 50 mM resulted in 20% or greater inhibition of H2 oxidation.The H2 uptake capacity of isolated 122 DES bacteroids (expressed on a dry bacteroid basis) was at least 10-fold higher than the rate of the nitrogenase reaction in nodules expressed on a comparable basis. Since about 1 mol of H2 is evolved for every mol of N2 reduced during the N2 fixation reaction, these observations explain why soybean nodules formed by strain 122 DES and other strains with high H2 uptake activities have a capacity for recycling all the H2 produced from the nitrogenase reaction.Abbreviations PMS PHenazine methosulfate - MB Methylene blue  相似文献   

4.
Hydrogen peroxide production by roots and its stimulation by exogenous NADH   总被引:4,自引:0,他引:4  
H2O2 production by roots of young seedlings was monitored using a non-destructive in vivo assay at pH 5.0. A particularly high rate of H2O2 production was measured in the roots of soybean (Glycine max L. cv. Labrador) seedlings which were used for further investigation of the physiological and enzymological properties of apoplastic H2O2 production. In the soybean root H2O2 production can be stimulated 10-fold by exogenous NADH or NADPH. This response displays typical features of a peroxidase-catalyzed oxidase reaction using NAD(P)H as electron donor for the reduction of O2 to H2O2. Comparative measurements showed that the NADH-induced H2O2 production of the roots resembles the H2O2-forming activity of horseradish peroxidase with respect to NADH and O2 concentration requirements and sensitivity to inhibition by KCN, NaN3, superoxide dismutase and catalase. NADH-induced H2O2 production can be observed with similar intensity in all regions of the root, in agreement with the distribution of apoplastic peroxidase activity. In contrast, the activity responsible for the basal H2O2 production in the absence of exogenous NADH was mainly confined to a short subapical zone of the root and differs from the NADH-induced reaction by insensitivity to inhibition by superoxide dismutase and a strikingly lower requirement for O2. It is concluded that the basal H2O2 production of the root is mediated by an enzyme different from peroxidase, possibly a plasma membrane O2?-producing oxidase.  相似文献   

5.
The effect of the antiarrhythmic drugs lidocaine, quinidine and procainamide on macrophage function was investigated in RAW 264.7 mouse monocytic macrophage cell. Cells stimulated by either zymosan or phorbol ester were found to generate both superoxide (O 2 ) and H2O2. The production of O2 was detected as superoxide dismutase inhibitable ferricytochrome c reduction. H2O2 production was monitored in both chemical and flow cytometric fluorescent assays. Although all three drugs inhibited both O2 and H2O2 release in a dose dependent manner, only quinidine was found to have significant inhibitory effects. The amounts of quinidine required to cause a 50% inhibition in O2 production in zymosan and phorbol ester stimulated cells were found to be 250 M and 300 M, respectively and the amounts required to cause one-half optimum levels of H2O2 production in these cells were found to be 50 M and 100 M, respectively. The effect of these drugs on O2 producing NADPH oxidase was investigated and only procainamide was found to have a significant effect (p<0.001) in inhibiting the oxidase activity. Lidocaine and quinidine had no significant effect on the activation of the respiratory burst oxidase. A sensitive and convenient differential phagocytosis assay was devised on the basis of number of particles engulfed by individual phagocytes using flow cytometric techniques. It appears to be remarkably free of interference and was applied to investigate the role of antiarrhythmic drugs on the phagocytosis of fluorescent latex beads. All three antiarrhythmic drugs inhibited phagocytosis of latex beads in a dose dependent manner irrespective of the number of particles phagocitized by the cells. The results of these studies do not conclusively establish a mechanism of action of these drugs on the generation of O2 and H2O2 by stimulated macrophages; nevertheless, it is interesting that all three drugs inhibited the phagocytic activity.  相似文献   

6.
Summary The enzymatic destruction of oxidizing products produced during metabolic reduction of oxygen in the cell (such as singlet oxygen, H2O2 and OH radical) involves the concerted action of superoxide dismutase-which removes O 2 - and yields H2O2-and H2O2 removing enzymes such as catalase and glutathione peroxidase. A difference in distribution or ratio of these enzymes in various tissues may result in a different reactivity of oxygen radicals.It was found that in red blood cells superoxide dismutase and catalase are extracted in the same fraction as hemoglobin, while glutathione peroxidase appears to be loosely bound to the cellular structure. This suggests that in red blood cells catalase acts in series with superoxide dismutase against bursts of oxygen radicals formed from oxyhemoglobin, while glutathione & peroxidase may protect the cell membrane against low concentrations of H2O2. On the other hand, catalase activity is absent in various types of ascites tumor cells, while glutathione peroxidase and superoxide dismutase are found in the cytoplasm. However, the peroxidase/dismutase ratio is lower than in liver cells, and this may provide an explanation for the higher susceptibility of tumor cells to treatments likely to involve oxygen radicals.  相似文献   

7.
The goal of the study was to investigate the effects of exogenous selenium (Se) on the tolerance of faba bean plants to lead (Pb) stress under P-deficient conditions. The bean plants were grown for 2 weeks on Hoagland solution supplied with Pb (0, 50 μM) and Se (0, 1.5, or 6 μM), separately or simultaneously. It was shown that Pb did not affect shoot growth but caused major damage in the leaves, which was accompanied by Pb accumulation in these tissues. The exposure of the shoots to Pb led to significant changes in the biochemical parameters: the MDA content, glutathione peroxidase (GSH-Px), guaiacol peroxidase (GPOX), and catalase (CAT) activity increased. Furthermore, Pb intensified O 2 ?? and H2O2 production. Both the Se concentrations used increased the chlorophyll b, chlorophyll a+b, and carotenoid content in the faba bean plants. Selenite also generally enhanced CAT, GPOX, and GSH-Px activities and the T-SH level. Our results imply that the degree of disturbances caused by Pb could be partially ameliorated by Se supplementation. Selenite at a lower dose alleviated Pb toxicity by decreased H2O2 and O 2 ?? production and decreased the GSH-Px, GPOX, and CAT activities. The beneficial effect of the higher selenite concentration could be related to reduction of lipid peroxidation in the shoots of the Pb-treated plants. However, the effect of Se on the Pb-stressed plants greatly depended on the selenite dose in the nutrient solution.  相似文献   

8.
Several abiotic factors cause molecular damage to plants either directly or through the accumulation of reactive oxygen species such as hydrogen peroxide (H2O2). We investigated if application of nitric oxide (NO) donor 2,2′-(hydroxynitrosohydrazono) bis-ethanimine (DETA/NO) could reduce the toxic effect resulting from short-term salt stress. Salt treatment (150 mM NaCl) alone and in combination with 10 μM DETA/NO or 10 μM DETA were given to matured soybean root nodules for 24 h. Salt stress resulted in high H2O2 level and lipid peroxidation while application of DETA/NO effectively reduced H2O2 level and prevented lipid peroxidation in the soybean root nodules. NO treatment increased the activities of ascorbate peroxidase and dehydroascorbate reductase under salt stress. Whereas short-term salt stress reduced AsA/DHAsA and GSH/GSSG ratios, application of the NO donor resulted in an increase of the reduced form of the antioxidant metabolites thus increasing the AsA/DHAsA and GSH/GSSG ratios. Our data suggests a protective role of NO against salt stress.  相似文献   

9.
Thermotoga hypogea is an extremely thermophilic anaerobic bacterium capable of growing at 90°C. It was found to be able to grow in the presence of micromolar molecular oxygen (O2). Activity of NADH oxidase was detected in the cell-free extract of T. hypogea, from which an NADH oxidase was purified to homogeneity. The purified enzyme was a homodimeric flavoprotein with a subunit of 50 kDa, revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It catalyzed the reduction of O2 to hydrogen peroxide (H2O2), specifically using NADH as electron donor. Its catalytic properties showed that the NADH oxidase had an apparent Vmax value of 37 mol NADH oxidized min–1 mg–1 protein. Apparent Km values for NADH and O2 were determined to be 7.5 M and 85 M, respectively. The enzyme exhibited a pH optimum of 7.0 and temperature optimum above 85°C. The NADH-dependent peroxidase activity was also present in the cell-free extract, which could reduce H2O2 produced by the NADH oxidase to H2O. It seems possible that O2 can be reduced to H2O by the oxidase and peroxidase, but further investigation is required to conclude firmly if the purified NADH oxidase is part of an enzyme system that protects anaerobic T. hypogea from accidental exposure to O2.  相似文献   

10.
An enzyme preparation from suspension cultured tobacco cells oxidized IAA only in the presence of added cofactors, Mn2+ and 2,4-dichlorophenol, and showed two pH optima for the oxidation at pH 4·5 and 5·5. Effects of various phenolic compounds and metal ions on IAA oxidase activity were examined. The properties of seven peroxidase fractions separated by column chromatography on DEAE-cellulose and CM-Sephadex, were compared. The peroxidases were different in relative activity toward o-dianisidine and guaiacol. All the peroxidases catalysed IAA oxidation in the presence of added cofactors. The pH optima for guaiacol peroxidation were very similar among the seven isozymes, but the optima for IAA oxidation were different. The anionic and neutral fractions showed pH optima near pH 5·5, but the cationic isozymes showed optima near pH 4·5. With guaiacol as hydrogen donor, an anionic peroxidase (A-1) and a cationic peroxidase (C-4) were very different in H2O2 concentration requirements for their activity. Peroxidase A-1 was active at a wide range of H2O2 concentrations, while peroxidase C-4 showed a more restricted H2O2 requirement. Gel filtration and polyacrylamide gel studies indicated that the three cationic peroxidases have the same molecular weight.  相似文献   

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